Isolation of a herpes simplex virus type 1 mutant with a deletion in the virion host shutoff gene and identification of multiple forms of the vhs (UL41) polypeptide.

The virion host shutoff (vhs) gene (UL41) of herpes simplex virus type 1 (HSV-1) encodes a virion component that induces degradation of host mRNAs and the shutoff of most host protein synthesis. Subsequently, the vhs protein accelerates the turnover of all kinetic classes of viral mRNA. To identify the vhs (UL41) polypeptide within infected cells and virions, antisera raised against a UL41-lacZ fusion protein were used to characterize the polypeptides encoded by wild-type HSV-1 and two mutants: vhs1, a previously characterized mutant that lacks detectable virion host shutoff activity, and vhs-delta Sma, a newly constructed mutant containing a deletion of 196 codons from UL41. Two forms of the vhs (UL41) polypeptide were identified in cells infected with the wild-type virus or vhs1. Wild-type HSV-1 produced a major 58-kDa polypeptide, as well as a less abundant 59.5-kDa form of the protein, while vhs1 produced 57- and 59-kDa polypeptides that were approximately equally abundant. Although for either virus, both forms of the protein were phosphorylated, they differed in the extent of phosphorylation. While both vhs polypeptides were found in infected cells, only the faster migrating, less phosphorylated form was incorporated into virions. vhs-delta Sma encoded a smaller, 31-kDa polypeptide which, although present in infected cells, was not incorporated into virions. The results identify multiple forms of the vhs (UL41) polypeptide and suggest that posttranslational processing affects its packaging into virions, as well as its ability to induce mRNA degradation.